Question

If sinx=4/5 and x is in quadrant 2, then tan2x=
-12/7
24/7
-24/7
12/7
I tried solving using a 3-4-5 triangle and got some answers that were very off. PLEASE HELP

Answer 1

I am pretty sure we have to use trig identities. I am not sure if we use sin2x or tan2x double identities to solve, or if it is totally different identities from that.

Answer 2

draw the triangle in quadrant 2 first

Answer 3

so tan x = -4/3

now you can use the formula for tan 2x

= 2 tan x
-------
1 - tan^2 x

Answer 4

(if my memory serves me right)

Answer 5

i'll check that out

Answer 6

yea thats correct
so plug in tanx = -4/3

Answer 7

so tan2x=2tan-4/3/1+tan2(-4/3)

Answer 8

no
tan 2x = (2 * -4/3)
---------
1 - (-4/3)^2

Answer 9

the -4/3 replaces the tan x

Answer 10

why is the denominator squared?

Answer 11

(-4/3)^2 ?
use your calculator

Answer 12

okay

Answer 13

I get tan2x=3.43

Answer 14

yes that is correct to 2 decimal places but they want the answer as a fraction

Answer 15

24/7

Answer 16

thats correct