Question

Pls I need it today
If cos A=3/5 and sin B=7/25,where A is acute and B is obtuse , find without using tables ,the values of cos (A+B)
Plsssss I need it now

Answer 1

first triangle 3,4, 5 in quad 1

second triangle 24, 7 , 25 in quad II

now look at it

with triangle similar to A in quadrant III but 8 tiems lengths

x = - 24, same as triangle A

y = -32

hypotenuse = 40

so

I have a triangle in Quadrant III with hypotenuse 40 and leg 24 along -x axis

what is angle below -y axis ?

cos T = -24/40 = -3/5

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