Question

Cho \(\dfrac{a}{3}\)=\(\dfrac{b}{5}\).Tính giá trị biểu thức C=\(\dfrac{5a^2+3b^2}{10a^2-3b^2}\)

Answer 1

Đặt \(\frac{a}{3}=\frac{b}{5}=k\)

=>a=3k; b=5k

\(C=\frac{5a^2+3b^2}{10a^2-3b^2}\)

\(=\frac{5\cdot\left(3k\right)^2+3\cdot\left(5k\right)^2}{10\cdot\left(3k\right)^2-3\cdot\left(5k\right)^2}=\frac{5\cdot9k^2+3\cdot25k^2}{10\cdot9k^2-3\cdot25k^2}=\frac{45k^2+75k^2}{90k^2-75k^2}\)

\(=\frac{120}{15}=8\)