Q. Prove that: (2cos2A-1)(2cos2A+1)(2cos4A-1)(2cos8-1)=2cos16A+1

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Q. Prove that : tan20 + 4sin20 = root 3 Soln: L.H.S. = tan20 + 4sin20 = sin20/cos20 + 4sin20 = (sin20 + 4sin20.cos20)/(cos20) = (sin20 + 2sin40)/cos20 = [sin20 + ...
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Q. If 7 times the 7th term of an AP is equal to 11 times its eleventh term, show that the 18th term of the AP is zero. Soln: Let first term = a and common difference = d in the AP. We have, nth term tn = a + (n -- 1)d Seventh term (t7) = a ...