# Maths

if COS A=3/5 and Sin B=7/25, when A us acute and B is obtuse, find without using tables. the value of COS(A+B)

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1. DDDDDDRAW IT !!!!!!!
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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Damon

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