<span>4х-3х+12=0
х+12=0
х=-12
Ответ: х=-12
</span>
3V6 = V3^2*6 =
= V9*6 = V54
1)2cos²x-5sinxcosx-3cos²x=0
cos²x+5sinxcosx=0 /cos²x≠0
1+5tgx=0
tgx=-1
x=-π/4+πn
2)3sin²x-4sinxcosx-5cos²x=0 /cos²x≠0
3tg²x-4tgx-5=0
tgx=a
3a²-4a-5=0
D=16+60=76 √D=2√19
a1=(4-2√19)/6=(2-√19)/3⇒tgx=(2-√19)/3⇒x=arctg((2-√19)/3)+πn
a1=(4+2√19)/6=(2+√19)/3⇒tgx=(2+√19)/3⇒x=arctg((2+√19)/3)+πn
Cos(180-30)/sin40-sin(180-30)/cos40=-cos30/sin40-sin30/cos40=
=-(cos30cos40+sin30sin40)/sin40cos40=-cos(40-30):1/2sin80=
<span>-cos10:1/2sin(90-10)=-cos10:1/2cos10=-2</span>