Sine Calculator
Calculate sine instantly with our math tool. Shows detailed work, formulas used, and multiple solution methods. Free to use with no signup required.
Formula
sin(theta) = opposite / hypotenuse
In a right triangle, sine equals the ratio of the side opposite the angle to the hypotenuse. On the unit circle, sin(theta) is the y-coordinate of the point at angle theta. The Taylor series is sin(x) = x - x^3/3! + x^5/5! - ...
Worked Examples
Example 1: Computing Sine of 30 Degrees
Problem: Find sin(30 degrees) and all related trigonometric function values.
Solution: sin(30) = 0.5 (exact: 1/2)\ncos(30) = sqrt(3)/2 = 0.8660\ntan(30) = 1/sqrt(3) = 0.5774\ncsc(30) = 1/sin(30) = 2\nsec(30) = 2/sqrt(3) = 1.1547\ncot(30) = sqrt(3) = 1.7321\nVerify: sin^2(30) + cos^2(30) = 0.25 + 0.75 = 1
Result: sin(30) = 0.50000000 | Quadrant I | Identity verified
Example 2: Inverse Sine Calculation
Problem: Find the angle whose sine is 0.7071.
Solution: arcsin(0.7071) = 45.0000 degrees\nThis is sqrt(2)/2, the sine of 45 degrees\nSecond solution: 180 - 45 = 135 degrees\nBoth sin(45) and sin(135) equal 0.7071\ncos(45) = 0.7071, cos(135) = -0.7071
Result: arcsin(0.7071) = 45.0000 deg (or 135.0000 deg)
Frequently Asked Questions
What is the sine function and what does it represent geometrically?
The sine function is one of the fundamental trigonometric functions. In a right triangle, sine of an angle equals the ratio of the opposite side to the hypotenuse: sin(theta) = opposite / hypotenuse. On the unit circle, sin(theta) represents the y-coordinate of the point where the terminal side of the angle intersects the circle. The sine function produces values between -1 and 1, oscillating smoothly as the angle increases. It has a period of 360 degrees (2 pi radians), meaning sin(theta + 360) = sin(theta). The graph of sine is the well-known sinusoidal wave, starting at zero, reaching a maximum of 1 at 90 degrees, returning to zero at 180 degrees, dropping to -1 at 270 degrees, and completing the cycle at 360 degrees.
What are the exact values of sine at standard angles?
The exact sine values at standard angles follow a memorable pattern. Sin(0) = 0, sin(30) = 1/2, sin(45) = sqrt(2)/2 (approximately 0.7071), sin(60) = sqrt(3)/2 (approximately 0.8660), and sin(90) = 1. A useful mnemonic is that these values equal sqrt(0)/2, sqrt(1)/2, sqrt(2)/2, sqrt(3)/2, and sqrt(4)/2 respectively. For angles beyond 90 degrees, use reference angles: sin(120) = sin(60) = sqrt(3)/2, sin(150) = sin(30) = 1/2, sin(180) = 0. In quadrant III and IV, sine is negative: sin(210) = -1/2, sin(300) = -sqrt(3)/2. Memorizing these exact values is essential for trigonometry, calculus, and physics courses where calculator use may be restricted.
How is the sine function computed using the Taylor series?
The Taylor series expansion of sine around zero is sin(x) = x - x^3/3! + x^5/5! - x^7/7! + x^9/9! - ..., where x is in radians and n! denotes n factorial. This infinite series converges for all real numbers, making it a universal method for computing sine to arbitrary precision. In practice, computers and calculators use optimized versions of this series along with range reduction techniques. First, the angle is reduced to the range [0, pi/4] using symmetry properties, then a truncated polynomial (usually a minimax polynomial) approximates sine in that range. For small angles, sin(x) is approximately equal to x (the first term alone), which is why the small-angle approximation is so widely used in physics and engineering for angles less than about 10 degrees.
What is the Pythagorean identity involving sine?
The most fundamental trigonometric identity is sin^2(x) + cos^2(x) = 1, known as the Pythagorean identity because it derives directly from the Pythagorean theorem. On the unit circle, the point (cos(x), sin(x)) lies on a circle of radius 1, so the sum of squares of coordinates equals 1. This identity is indispensable in simplifying trigonometric expressions, solving equations, and performing substitutions in calculus. For example, if sin(x) = 3/5, then cos(x) = plus or minus 4/5 (the sign depends on the quadrant). The identity extends to two other forms by division: dividing by cos^2 gives 1 + tan^2 = sec^2, and dividing by sin^2 gives 1 + cot^2 = csc^2. Sine Calculator verifies the identity numerically for any input angle.
In which quadrants is the sine function positive and negative?
The sine function is positive in quadrants I and II (0 to 180 degrees) and negative in quadrants III and IV (180 to 360 degrees). This follows from the unit circle definition where sine represents the y-coordinate: points above the x-axis have positive y-coordinates (quadrants I and II), while points below have negative y-coordinates (quadrants III and IV). The mnemonic ASTC (All Students Take Calculus) helps remember which functions are positive: All in Q1, Sine in Q2, Tangent in Q3, Cosine in Q4. Understanding sign patterns is crucial for solving trigonometric equations, as each equation like sin(x) = 0.5 has two solutions per period: x = 30 degrees (Q1) and x = 150 degrees (Q2). The reference angle (acute angle to the nearest x-axis) determines the magnitude.
How is sine used in the Law of Sines for solving triangles?
The Law of Sines states that in any triangle, a/sin(A) = b/sin(B) = c/sin(C), where lowercase letters are sides and uppercase letters are opposite angles. This law is essential for solving triangles in two cases: ASA (two angles and the included side) and AAS (two angles and a non-included side). For example, if A = 40 degrees, B = 60 degrees, and a = 10, then b = 10 sin(60)/sin(40) = 13.47. The Law of Sines also applies in the ambiguous SSA case (two sides and a non-included angle), where zero, one, or two triangles may be possible. The law can be proved by dropping an altitude in any triangle and expressing its length in two ways using sine. It is one of the most frequently used formulas in surveying, navigation, and engineering.