Question

Giải các phương trình sau:
a) \(2^{x+4}+2^{x+2}=5^{x+1}+3.5^x\);
b) \(5^{2x}-7^x-5^{2x}.17+7^x.17=0\);
c) \(4.9^x+12^x-3.16^x=0\)
d) \(-8^x+2.4^x+2^x-2=0\)

Answer 1

a) \(2^{x+4}+2^{x+2}=5^{x+1}+3\cdot5^x\)

\(\Rightarrow2^x+2^4+2x^x+2^2=5^x\cdot x+3\cdot5^x\)

\(\Leftrightarrow2^x+16+2^x\cdot4=5\cdot5^x+3\cdot5^x\)

\(\Leftrightarrow16\cdot2^x+4\cdot2^x=8\cdot5^x\)

\(\Leftrightarrow20\cdot2^x=8\cdot5^x\)

\(\Leftrightarrow20\cdot\left(\dfrac{2}{5}\right)^x=8\)

\(\Leftrightarrow\left(\dfrac{2}{5}\right)^x=\dfrac{2}{5}\)

\(\Leftrightarrow\left(\dfrac{2}{5}\right)^x=\left(\dfrac{2}{5}\right)^1\)

\(\Rightarrow x=1\)