an angle question

[fast bridge]

The question is if tan x =-3/4 and the angle is in the second half find sin x and cos x

[harsh prism]

it's a trigonometric identity
sin²x + cos²x = 1

[fast bridge]

I know

But why cos²x(9/16 + 1) =1

Here's what I did

[harsh prism]

they factored out cos²x

[fast bridge]

Oh

Thanks

[harsh prism]

urwelcome

[fast bridge]

But