Using the cosine double angle formula,

(Note I took the positive case since
terminates in the first quadrant)
Using the Pythagorean identity,

(Note I took the positive case since
terminates in the first quadrant)
Basically the answer is 6, if you'd like an explanation, let me know. :)
Answer:
y = 5x - 4
for the x values..
y = -4
y = 1
y = 6
Step-by-step explanation: