Question

ECUATII EXPONENTIALE

VA ROG AJUTATI-MA!

Answer 1

${7}^{x + 2} - 3 \times {7}^{x + 1} - 20 \times 7= 392$

${7}^{x} \times {7}^{2} - 3 \times {7}^{x} \times 7 - 20 \times 7= 392$

$49 \times {7}^{x} - 21 \times {7}^{x} - 20 \times 7 = 392 \: | \div 7$

$7 \times {7}^{x} - 3 \times {7}^{x} - 20 = 56$

$7 \times {7}^{x} - 3 \times {7}^{x} = 56 + 20$

$7 \times {7}^{x} - 3 \times {7}^{x} = 76$

${7}^{x} (7 - 3) = 76$

${7}^{x} \times 4 = 76 \: | \div 4$

${7}^{x} = 19$

$ln {7}^{x} = ln19$

$xln7 = ln19$

$x = \frac{ln19}{ln7}$