Question

(i) The value of a, if the value of - x2 + 3x -a is equal to 8, when x = -1, is
(a) 12
(6) 14
(c) 15
(d) - 12​

Answer 1

Answer:

$-\left(-1\right)\cdot \:2+3\left(-1\right)-a=8\quad :\quad a=-9$

Step-by-step explanation:

Given :

x = -1

adding it in the equation be

$-\left(-1\right)\cdot \:2+3\left(-1\right) - a$

To Find:

value of a

Solution:

$-\left(-1\right)\cdot \:2+3\left(-1\right)-a=8$

$\mathrm{Remove\:parentheses}:\quad \left(-a\right)=-a,\:-\left(-a\right)=a$

$1\cdot \:2-3\cdot \:1-a=8$

$\mathrm{Multiply\:the\:numbers:}\:1\cdot \:2=2$

$2-3\cdot \:1-a=8$

$\mathrm{Multiply\:the\:numbers:}\:3\cdot \:1=3$

$2-3-a=8$

$\mathrm{Subtract\:the\:numbers:}\:2-3=-1$

$-a-1=8$

$\mathrm{Add\:}1\mathrm{\:to\:both\:sides}$

$-a-1+1=8+1$

$-a=9$

$\mathrm{Divide\:both\:sides\:by\:}-1$

$\frac{-a}{-1}=\frac{9}{-1}$

$a=-9$