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If 10tanA.tanB = 9, what is the value of cos(A – B)/cos(A + B)?1). 12). 03). 194). 9/10 |
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Answer» We know, COS(A – B) = cosAcosB + sinAsinB And, cos(A + B) = cosAcosB – sinAsinB Given, tanAtanB = 9/10 cos(A – B)/cos(A + B) ⇒ (cosAcosB + sinAsinB)/(cosAcosB – sinAsinB) ⇒ (1 + tanAtanB)/(1 – tanAtanB) ⇒ (1+ 9/10)/(1 – 9/10) ⇒ 19 ∴ cos (A – B)/cos (A + B) = 19 |
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