Exact
0
Cos 90 Degrees
Answer
cos 90° equals 0, which is 0 as a decimal.
Decimal
0
Formula
cos 90° = 0
Worked steps
1
Right-triangle definition
In a right triangle, cos(angle) = adjacent side ÷ hypotenuse. At 90°, the adjacent side has zero length, so cos 90° = 0.
2
Calculator method (DEG mode)
Set the calculator to DEG. Press cos, type 90, press =. Result: 0.
3
Calculator method (RAD mode)
Convert 90° to radians first: 90 × π / 180 = 1.570796 rad. Then cos of that gives 0.
About this value
Cos 90° is a standard trigonometric value. The exact form is 0; the decimal 0 is what a calculator returns. At 90° the adjacent side has zero length, so cosine is exactly zero — the cosine curve crosses the x-axis here.
Frequently asked questions
What is cos 90 degrees?
Cos 90 Degrees equals 0 as an exact value, or 0 as a decimal. The exact form is what you'd typically write in exam working; the decimal is what your calculator displays.
How do I enter this on a calculator?
Set the angle mode to DEG. Press cos, type the angle, press =. If your calculator is in RAD mode by mistake, you will get a different answer — always check the mode pill before pressing a trig function.
Why memorise the standard angle values?
The values for 30°, 45°, 60°, and 90° appear in almost every trigonometry problem at school level. Knowing the exact form (with surds) lets you produce surd-form answers expected in exams, instead of decimal approximations.
What is this in radians?
To convert the angle to radians, multiply by π/180. The function value is the same regardless of mode — the answer for 90° is 0 in DEG or sin(angle_in_rad) of the equivalent radian measure.