Question

Trig question for tan(a+b)

evaluate the expression given that cos a=4/5 with 0 11 years ago

Answer 1

for the tan sum formula

i'm getting -9/8 for the numerator

Answer 2

but the denominator im not sure

Answer 3

is it 77/32..?

Answer 4

@Nnesha @freckles

Answer 5

@sleepyjess

Answer 6

\[\tan(a+b)=\frac{ \sin(a+b)}{ \cos(a+b) }\]

Answer 7

\[\sin(a+b)=sina*cosb+sinb*cosa\]

Answer 8

\[\cos(a+b)=cosa*cosb-sina*sinb\]

Answer 9

if the sinb is -15/17 when b is in IV quater, then sinb=15/17 when b is in I and II quaters

Answer 10

can we use this formula

Answer 11

got tanA=3/4
tanb=-15/8

Answer 12

yes we can, but we are given cos and sin, so i used what i wrote

Answer 13

but im plugging it in wrong or something because the answer i got is -36/77 but the answer key was 117/4

Answer 14

what are you getting?

Answer 15

that's true i also got that. I don't know then. sorry
maybe these can help @SolomonZelman @TheSmartOne @amistre64 @freckles @perl

Answer 16

the answer key is probably wrong

Answer 17

I wouldn't be suprised if it is

Answer 18

maybe.

Answer 19

ill stick with my answer

Answer 20

ty

Answer 21

np :)

Answer 22

@dtan5457 what did you get for sin(a) and cos(b)?

Answer 23

3/5, 8/17, but i still used the tan formula

Answer 24

ok that is great so
tan(a)=sin(a)/cos(a)=3/4
and
tan(b)=sin(b)/cos(b)=-15/17

Answer 25

or these the numbers you input?

Answer 26

oops -15/8*

Answer 27

yeah

Answer 28

final answer i got was -36/77

Answer 29

can you confirm?

Answer 30

\[\frac{\frac{3}{4}-\frac{15}{8}}{1-\frac{3}{4} \frac{-15}{8}}=\frac{8(3)-4(15)}{4(8)+3(15)} \\ =\frac{24-60}{32+45}=\frac{-36}{77}\]

Answer 31

always knew i was right