(sinx)⁻¹+(tgx)⁻¹=1/sinx+cosx/sinx=(1+cosx)/sinx=
=(sin²(x/2)+cos²(x/2)+cos²(x/2)-sin²(x/2))/(2*sin(x/2)*cos(x/2))=
=2*cos²(x/2)/(2*sin(x/2)*cos(x/2))=cos(x/2)/sin(x/2)≡ctg(x/2).
Sin2a = 2sina*cosa
sin^2 a = 1 - cos^2 a = 1 - 64/289 = 225/289
sina = +- 15/17, но т.к. -pi/2 < A < 0, где sin < 0, то sina = - 15/17
sin2a = 2*8/17*(-15/17) = - 240/289
Все просто! 100*100:5=2000 - целое.
Ответ: 2000
Или
1) 100*100= 10000
2) 10000:5= 2000
Ответ: 2000
<span>320/(52-x)=8 </span>
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