3x-5-7+4x=2; 3x+4x=2+7+5; 7x=14; x=14/7=2. Ответ: x=2.
Cos4a=1-2sin²2a=1-2*0,36=1-0,72=0,28
<span>log3(x^2-11x+27)=2</span>
<span><span>log3(x^2-11x+27)=log3 9</span></span>
<span><span>(x^2-11x+27=9</span></span>
<span><span>x^2-11x+18=0</span></span>
<span><span>x1=9</span></span>
<span><span>x2=2</span></span>
15/(x-1.5)-18/(x+1.5)=0.5
(15/(x-1.5)-18/(x+1.5))*(x-1.5)=0.5*(x-1.5)
(-6x+99)/(2x+3)=0.5x-0.75
(-6x+99)/(2x+3)*(x+1.5)=(0.5x-0.75)*(x+1.5)
-3x+49.5=0.5x²-1.125
-0.5x²-3x+50,625=0
x1=-13.5 x2=7.5
7.5+1.5=9
7.5-1.5=6
18/9=2
15/6=2.5
2.5-2=0.5
15/(x-1.5)-18/(x+1.5)=0.5
-0.5x²-3x+50,625=0
x1=-13.5
x2=7.5
Ответ: 7,5 км в час