Question

Given that sin θ = 3/4 and θ is in Quadrant II: Find cos θ.

Answer 1

this is for the Sin

*Remember that sin = opposite / hypotenuse*

a² + b² = c² (where a and b are legs and c is the hypotenuse)

From the picture, you can see:

a = 3

c = 4

Plug these into the equation and solve for b.

* a² + b² = c² *

step 1: 3² + b² = 4²

step 2: 9 + b² = 16

step 3: b² = 16 - 9

step 4: b² = 7

step 5: √(b²) = √7

step 6: b = ± √7

FOR COS:

From the picture,  you can see that if θ is in quadrant II, b has to be negative.

b = -√7 = adjacent

Remember that cos θ = adjacent / hypotenuse.

cos θ = adjacent / hypotenuse

cos θ = (-√7 / 4)