Question

sendo f(x)=2x²-5x determine :
a) f(√3);

b)os valores de X para f(x)=21.


me ajudem pfvr.​

Answer 1

a)

$f(x) = 2 {x}^{2} - 5x \\ f( \sqrt{3}) = 2. {( \sqrt{3}) }^{2} - 5. \sqrt{3} \\ f( \sqrt{3} ) = 2.3 - 5 \sqrt{3} \\ f( \sqrt{3}) = 6 - 5 \sqrt{3}$

b)

$2 {x}^{2} - 5x = 21 \\ 2 {x}^{2} - 5x - 21 = 0$

$Δ = {( - 5)}^{2} - 4.2.( - 21) \\ Δ = 25 + 168 \\ Δ = 193$

$x = \frac{ - ( - 5)± \sqrt{193}}{2.2} \\ x = \frac{5 ± \sqrt{193} }{4}$

$x' = \frac{5 + \sqrt{193} }{2} \\ x'' = \frac{5 - \sqrt{193} }{2}$