Question

Sendo  A= 3x² +5x -6, determine o valor de A para

a) X= -2    b) x=2-¹

Answer 1

a) $A = 3x^{2}+5x-6 \\\\ A = 3 \cdot (-2)^{2}+5 \cdot (-2) -6 \\\\ A = 3 \cdot 4-10-6 \\\\ A = 12-10-6 \\\\ \boxed{\boxed{A = -4}}$


b) $A = 3x^{2}+5x-6 \\\\ A = 3 \cdot (2^{-1})^{2}+5 \cdot (2^{-1})-6 \\\\ A = 3 \cdot 2^{-2}+5 \cdot 2^{-1}-6 \\\\ A = 3 \cdot (\frac{1}{2})^{2}+5 \cdot (\frac{1}{2})-6 \\\\ A = 3 \cdot \frac{1}{4}+\frac{5}{2}-6 \\\\ A = \frac{3}{4}+\frac{10}{4}-\frac{24}{4} \\\\ \boxed{\boxed{A = -\frac{11}{4}}}$

Answer 2

A= 3x² +5x - 6

a) x = - 2 ⇒ A= 3.(- 2)² +5.(- 2) - 6 ⇒ A = 3.4 - 5.2 - 6 ⇒ A = 12 - 10 - 6 = - 4

b) x = 2⁻¹ ⇒ A= 3.(2⁻¹)² +5.(2⁻¹) - 6 ⇒ A = 3.2⁻² + 5.(2⁻¹) - 6 ⇒ A = 3/4 + 5/2 - 6
                                                   ⇒ A = (3 + 10 - 24)/4 = - 11/4