281)If A, B, and C are the angels of a △ABC then the following is equal to :
sin\(({B+C \over2})\)
282)the value of \(sin^21°+sin^25°+sin^29°+............... +sin^289°\):
\(11{1\over2}\)
283)The value of (1 + sec20° + cot70°)(1 - cosec20° + tan70°) is:
284)The value of cos24° + cos55° + cos125° + cos204° + cos 300° is
0.5
285)The value of cos20° + cos40° + cos60° + ...... + cos160° + cos180°
-1
286)The value of \(cot{π\over 20}.cot{3π\over 20}.cot{5π\over 20}.cot{7π\over 20}.cot{9π\over 20}\) is
287)If x & y are acute angle, x+y <90° & sin(2x - 20°) = cos(2y + 20°), the value of sec(x + y) is
288)If A & B are complementary angles, then the value of sinA.cosB + cosA.sinB - tanA.tanB + sec2A - cot2B is
289)If cosec39° = x, the value of \({1 \over cosec^251°}+sin^239°+tan^251°-{1 \over sin^2 51°sec^2 39°} \) is
290)If sin(A+B-C) = cos(A+C-B) = tan(B+C-A), then the value of angle A is