<span>1)sin 15' *cos 30' + sin 15'*cos 30'</span>
<span><span>)sin(15+30)=45</span></span>
<span><span><span>sin45=
</span></span></span>
<span><span><span> --------------------</span></span></span>
<span><span><span> 2</span></span></span>
<span><span><span>2</span></span></span>)sin 70' cos 40' - sin 40' cos 70'=
)sin(70-40)=30
sin30=1/2
я применла формулу
sin(α + β) = sin α cos β + cos α sin β
и точно также со знаком минус
{4х-у=2. |•3
{х+3у=20
{12х-3у=6
+
{х+3у=20
_______
13х=26
х=26:13
х=2
2+3у=20
3у=20-2
3у=18
у=6
ответ(2;6)
1) (4a-b^2)^2 =16а^2-8аb^2+b^4
2) (x^4 - 9x )^2 =x^8-18x^5+81x^2
3) (a-4) (a+4) =a^-16
4) (4 - x^2) (4 +x^2)=16-x^4