18
x>0
log(2)log(√3)x=2
log(√3)x=4
x=9
19
x>0
log(2)x=a
a²-4a+3=0
a1+a2=4 U a1*a2=3
a1=1⇒log(2)x=1⇒x=2
a2=3⇒log(2)x=3⇒x=8
20
x>0
9lg²x-10lgx+1=0
lgx=a
9a²-10a+1=0
D=100-36=64
a1=(10-8)/18=1/9⇒lgx=1/9⇒x=![\sqrt[9]{10}](https://tex.z-dn.net/?f=+%5Csqrt%5B9%5D%7B10%7D+ "\sqrt[9]{10}")
a2=(10+8)/18=1⇒lgx=1⇒x=10
21
x+3>0⇒x>-3
x-1>0⇒x>1
x∈(1;∞)
log(4)(x+3)/(x-1)=log(4)2
(x+3)/(x-1)=2
x+3=2x-2
2x-x=3+2
x=5
22
2x-1>0⇒x>1/2
x-9>0⇒x>9
x∈(9;∞)
lg√(2x-1)(x-9)=1
√(2x-1)(x-9)=10
2x²-18x-x+9-100=0
2x²-19x-91=0
D=361+728=1089
x1=(19-33)/4=-3,5не удов усл
x2=(19+33)/4=13