Question

If the point P(-3/5,y)lies on the unit circle and P is in the second quadrant, what does y equal

Answer 1

Y=4/5

Explanation:

This is a 3, 4, 5 right triangle, and since it is isn’t he second quadrant x is negative but y is positive.

Answer 2

If P(x, y) lies on the unit circle, then the distance from P to the origin must be 1:

√(x² + y²) = 1

x² + y² = 1

(– 3/5)² + y² = 1

(9/25) + y² = 1


Multiply both sides by 25:

9 + 25y² = 25


Solve the equation for y:

25y² = 25 – 9

25y² = 16

y² = 16/25

y² = (4/5)²


Take the square root of both sides:

y = ± √(4/5)²

y = ± 4/5


Since P is in the second quadrant, then y must be positive:

y > 0


So,

y = 4/5 <——— this is the answer.


I hope this helps. =)