Question

The point (3, -4) is on the terminal side of an angle theta. What is cos of theta?

Answer 1

3/5 because cos∆ = B/H

Answer 2

If the point (3-4) is on the terminal side of an angle Ф,we have a triangle where:
opposite side to Ф=-4
adjacent side to Ф=3

We have to calculate the radius (=hypotenuse)
Pythagoras theorem:
hypotenuse²=side₁²+side₂²
hypotenuse²=(-4)²+3²
hypotenuse²=16+9
hypotenuse²=25
hypotenuse=√25
hypotenuse=5

cos Ф= adjacent /hypotenuse

Data:
adjacent=3
hypotenuse=5

cos Ф=3/5

Answer: cos Ф=3/5