Cos 75*sin 345=cos(90-15)*sin(360-15)=sin15*(-sin15)=-sin²15=-sin²(60-45)=
=-(sin60*cos45-cos60*sin45)²=-(√3/2 *√2/2 - 1/2 *√2/2)²=-√2(√3-1)²/16
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(5a-21)/2=5a+4/1
(5a-21)*1=(5a+1)*2
5a-21=10a+2
5a-10a=2+21
-5a=23:(-5)
x=-4,6
Решение
<span>1) Sinx = - 1
x = - </span>π/2 + 2πk, k ∈ Z<span>
2) cosx = </span>√<span>2\2
x = + - arccos(</span>√2/2) + 2πn, n ∈ Z
x = + - π/4<span> + 2πn, n ∈ Z</span><span>
3) tgx = -</span>√<span>3
</span>x = arctg(- √3) + πk, k ∈ Z
x = - π/3 + πk, k ∈ Z