Question 1145659
If cos β = - 3/5 then, without a calculator, find cos(𝛑/2 - β). 
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cos(𝛑/2 - β) = sin(β)
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{{{sin(B) = sqrt(1 - cos^2(B)) = 4/5 or -4/5
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Cos is negative in Q2 and Q3.
Sin is positive in Q2 and negative in Q3