30/(27+x)+30/(27-x)=2.25
30(27-x)+30(27+x)=2.25(27+x)(27-x)
810-30x+810+30x=(60.75+2.25x)(27-x)
1620=1640.25-60.75x+60.75x-2.25x²
2.25x²=1640.25-1620
2.25x²=20.25
x²=9
x=3
отв:3км/ч
А)(a-6)(a+6)+(a+6)²+10a
a²-36+a²+12a+36+10a
2a²+22a
б)4m³-4(m+2)(4-2m+m²)=4m³-4(m+2)(m²-2m+4)=4m³-4*m³+8=4m³-4m³+8=8
2х-3у=1|*1=2х-3у=1
3х+у=7|*3=9х+3у=21
2х+9х=21+1
11х=22
х=2
2*2-3у=1
4-3у=1
3у=3
у=1
<span>2 Sin 15' Cos 15 = sin30 = 0,5</span>