Mình làm 5 câu thôi nhé !:
1) \(7^x\cdot49=7^{90}\)

\(\Rightarrow7^x\cdot7^2=7^{90}\)

\(\Rightarrow7^{x+2}=7^{90}\)

\(\Rightarrow x=90-2\)

\(\Rightarrow x=88\)

2) \(2^x\cdot4=128\)

\(\Rightarrow2^x\cdot2^2=2^7\)

\(\Rightarrow2^{x+2}=2^7\)

\(\Rightarrow x=7-2\)

\(\Rightarrow x=5\)

3) \(3^x-1=2^4\cdot5\)

\(\Rightarrow3^x=80+1\)

\(\Rightarrow3^x=81\)

\(\Rightarrow3^x=3^4\)

\(\Rightarrow x=4\)

4) \(3^x+15=42\)

\(\Rightarrow3^x=42-15\)

\(\Rightarrow3^x=27\)

\(\Rightarrow3^x=3^3\)

\(\Rightarrow x=3\)

5) \(4\cdot2^x-3=125\)

\(\Rightarrow2^2\cdot2^x=128\)

\(\Rightarrow2^{x+2}=2^7\)

\(\Rightarrow x=7-2\)

\(\Rightarrow x=5\)

6) 

\(5^x=5^{15}:5^3\\ \Leftrightarrow5^x=5^{15-3}\\ \Leftrightarrow5^x=5^{12}\\ \Leftrightarrow x=12\)

7) 

\(4^x=4^{15}:16\\ \Leftrightarrow4^x=4^{15}:4^2\\ \Leftrightarrow4^x=4^{15-2}\\ 4^x=4^{13}\\ \Leftrightarrow x=13\)

8) 

\(7^x=7^{20}:7^{10}\\ \Leftrightarrow7^x=7^{20-10}\\ \Leftrightarrow7^x=7^{10}\\ \Leftrightarrow x=10\)

9) 

\(11^x=11^{11}:11\\ \Leftrightarrow11^x=11^{11-1}\\ \Leftrightarrow11^x=11^{10}\\ \Leftrightarrow x=10\)

10)

\(3^{15}.3^x=3^{30}\\ \Leftrightarrow3^x=3^{30}:3^{15}\\ 3^x=3^{30-15}\\ \Leftrightarrow3^x=3^{15}\\ \Leftrightarrow x=15\)

11)

\(10+2x=4^5:4^3\\ \Leftrightarrow10+2x=4^2\\ \Leftrightarrow2x=6\\ \Leftrightarrow x=3\)

12)

\(20+5x=5^5:5^3\\ \Leftrightarrow20+5x=5^2\\ \Leftrightarrow5x=5\\ \Leftrightarrow x=1\)

13)

\(4x-20=2^5:2^2\\ \Leftrightarrow4x-20=2^3\\ \Leftrightarrow4x=28\\ \Leftrightarrow x=12\)

14)

\(15+2x=3^{80}:3^{77}\\ \Leftrightarrow15+2x=3^3\\ \Leftrightarrow2x=12\\ \Leftrightarrow x=6\)

giải giúp mik

\(3^{x+4}+3^x=2214\Rightarrow3^x.81+3^x=2214\Rightarrow3^x.\left(81+1\right)=2214\Rightarrow3^x.82=2214\Rightarrow3^x=27=3^3\Rightarrow x=3\)

\(3^{x+4}+3^x=2214\Leftrightarrow3^x\left(3^4+1\right)=2214\)

\(\Leftrightarrow3^x=27\Leftrightarrow x=3\)

\(\left(3x+4\right)^2+\left(5-3x\right)^2+2.\left(3x+4\right)\left(5-3x\right)\\ =\left[\left(3x+4\right)+\left(5-3x\right)\right]^2\\ =\left(3x+4+5-3x\right)^2\\ =9^2=81\)

=(3x+4+5-3x)^2

=9^2=81

hinh nhu la de bi sai 

x(1-3x)(4-3x)-(x-4)(3x+5)=(x-3x²)(4-3x)-(x-4)(3x+5)

                                       =(4(x-3x²)-3x(x-3x²))-(3x(x-4)+5(x-4))

                                       = (4x-12x²-3x²+9x³)-(3x²-12x+5x-20)

                                       = (9x³-15x²+4x)-(3x²-7x-20)

                                       = 9x³-15x²+4x-3x²-7x-20

                                       = 9x³-18x²+x-20

\(A=\left(\dfrac{6x+4}{3\sqrt{3x^3}-8}-\dfrac{\sqrt{3x}}{3x+2\sqrt{3x}+4}\right).\left(\dfrac{1+3\sqrt{3x^3}}{1+\sqrt{3x}}-\sqrt{3x}\right)\)

Điều kiện tự làm nha:

Đặt \(\sqrt{3x}=a\) thì ta có:

\(A=\left(\dfrac{2a^2+4}{a^3-8}-\dfrac{a}{a^2+2a+4}\right).\left(\dfrac{1+a^3}{1+a}-a\right)\)

\(=\left(\dfrac{2a^2+4}{\left(a-2\right)\left(a^2+2a+4\right)}-\dfrac{a}{a^2+2a+4}\right).\left(\dfrac{\left(1+a\right)\left(1-a+a^2\right)}{1+a}-a\right)\)

\(=\dfrac{a^2+2a+4}{\left(a-2\right)\left(a^2+2a+4\right)}.\left(1-2a+a^2\right)\)

\(=\dfrac{\left(a-1\right)^2}{a-2}=\dfrac{\left(\sqrt{3x}-1\right)^2}{\sqrt{3x}-2}\)

A) \(-4x2xy^2+3x^2.\frac{1}{3}y+\left(-5\right)xy.\frac{1}{5}xy=-8x^2y^2+x^2y+\left(-x^2y^2\right)=-9x^2y^2+x^2y\)

B) \(\frac{4}{3}x^4y^7-3x^4y^7=\frac{-5}{3}x^4y^7\)

C) \(\frac{2}{3}x^3y^4+3x^3y^4=3\frac{2}{3}x^3y^4\)

CHÚC BN HỌC TỐT!!!

\(\left(3x+2\right)\left(3x-2\right)=9x^2-4\)

-> chọn D