Question

[╰❥ɕɦáռ ռɦư ɕσռ ɠıáռᴾᴿᴼシ]

Tính giá trị biểu thức 

D=5.x²-7.x+1/3.x-1 với |x|=1/2

GIÚP MK VỚI!!!!!

Answer 1

[Huỳnh Quang Sang]

\(\left|x\right|=\frac{1}{2}\)nên \(x=\frac{1}{2}\)hoặc \(x=-\frac{1}{2}\)

• Tại \(x=\frac{1}{2}\): \(D=5\cdot\left[\frac{1}{2}\right]^2-7\cdot\frac{1}{2}+\frac{1}{3}\cdot\frac{1}{2}-1\)

\(=5\cdot\frac{1}{4}-\frac{7}{2}+\frac{1}{6}-1=\frac{5}{4}-\frac{7}{2}+\frac{1}{6}-1=\frac{5}{4}-\frac{14}{4}+\frac{1}{6}-1=-\frac{37}{12}\)

• Tại \(x=-\frac{1}{2}\): \(D=5\cdot\left[-\frac{1}{2}\right]^2-7\cdot\left[-\frac{1}{2}\right]+\frac{1}{3}\cdot\left[-\frac{1}{2}\right]-1\)

\(=5\cdot\frac{1}{4}-\left[-\frac{7}{2}\right]+\left[-\frac{1}{6}\right]-1\)

\(=5\cdot\frac{1}{4}+\frac{7}{2}+\left[-\frac{1}{6}\right]-1\)

\(=\frac{5}{4}+\frac{7}{2}+\left[-\frac{1}{6}\right]-1=\frac{43}{12}\)