SOLUTION: If cos α = -24/25 and sin ß = 4/5, α in quadrant II and ß in quadrant I, what is cos(α + ß)?

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Question 979153: If cos α = -24/25 and sin ß = 4/5, α in quadrant II and ß in quadrant I,
what is cos(α + ß)?
Answer by anand429(138) About Me  (Show Source):
You can put this solution on YOUR website!
cos a = -24/25
So, sin a = sqrt%281-cos%5E2%28a%29%29
= 7/25 (Taking positive value since, a is in quadrant II
Similarly,
cos b = sqrt%281-sin%5E2%28b%29%29
= 3/5 (since b in quadrant I)
cos(a+b) = cosa*cosb - sina*sinb
= %28-24%2F25%29%2A%283%2F5%29+-+%287%2F25%29%2A%284%2F5%29
=-4%2F5