Question

If the point P(-4/5, y) is on the unit circle in quadrant II, then y = ?

Answer 1

what do we know about a unit circle? and right triangles?

Answer 2

The unit circle is -1 to 1 on the x and y axis. x is correlated to cos and y is correlated to sin. The unit circle, in order, goes from 0, pi/2, pi, 3pi/2, and back to 2pi. There are the "30, 60, 90" and "45, 45, 90" right triangles

Answer 3

i wish i could draw at the moment ...

a unit circle is such that x^2 + y^2 = 1, might be the simplest formulaic way to explain this

Answer 4

Oh, I see, so plug in -4/5 and solve for y, basically.

Answer 5

yep

Answer 6

since we are in quadrant 2, x is negative and y is postive in order to verify the solution

Answer 7

one of the most use right triangles in problems is a 3,4,5

legs of 3 and 4, with a hypot of 5

if we scale your setup by 5 notice that:

-4/5, y, 1 --> -4, 5y, 5

hence 5y has to equal 3 in this instance

Answer 8

but the formulaic way is fine, this other stuff is just another way to look at it

Answer 9

I see. Thanks!

Answer 10

yw