if sin x = 3/5, find cos x

Answer 1

Joshua's answer is entirely correct, but it is probably worth mentioning that the triangle involved is the

right triangle with the simplest Pythagorean triple sides, namely, 3-4-5, a triangle which will be frequently encountered in math problems.

Answer 2

cosx = 4/5 or -4/5

could be either +4/5

sinx = 3/5 in either quadrant I or II

but cosx = 4/5 in quadrant I or IV

and cosx = -4/5 in quadrant II or III

adjacent side squared = hypotenuse side squared minus opposite side squared

A^2 = H^2 - O^2

A^2 = 5^2 -3^2 = 25-9 = 16

A= + or - sqr16 = + or - 4

cosx = +4/5 or -4/5

Answer 3

i personally draw a triangle for this equation as you know sin is opposite/ hypotenuse

that leaves the adjacent side be 4 once you perform the Pythagorean theorem (3^2+x^2=5^2)

now we know all sides, we know cos is adjacent over hypotenuse giving us 4/5