А) 15×(12+13+21)= 690
б) 50 × ( 80 - 60 +31)= 2550
в) 27 × ( 18 + 13 + 14) = 1215
45/4х-10х=8
5/4х=8
х=8:5/4
х=32/5
Task/27151545
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<span>(cos5a+5cos3a+10cosa)/(cosa)^5=
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</span>решение :<span>
* * * cos</span>²φ =(1+cos2φ)/2 ; cosα*cosβ =( cos(α+β)+ cos(α-β) )/2 * * *
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cos⁵α =(cosα)*(cos²α)² =(cosα)* ( (1+cos2α) /2 )² =(cosα)* (1+2cos2α+cos²2α)/4 = (cosα)*(1+2cos2α+(1+cos4α)/2 )/4 =
(cosα)*(3 +4cos2α +cos4α*cosα)/8=(3cosα+4cos2α*cosα +cos4α*cosα) /8=(3cosα+2cosα+2cos3α +(cos5α+cos3α)/2)/8 =(cos5α+5cos3α+10cosα)/16 .
Следовательно :
(cos5α+5cos3α+10cosα) / (cos⁵α ) =
(cos5α+5cos3α+10cosα) / ( (cos5α+5cos3α+10cosα)/16 ) = 16.
ответ: 16
1 4/5 х 4 5/6 - 1 4/5 + 3 1/5=1 4/5 (4 5/6 - 3 5/6) + 3 1/5= 1 4/5 х 1 + 3 1/5=
= 9/5 + 16/5= 25/5=5