Question

For the linear function f (x) = mx + b, f (-3) = 23 and f (2) = -7.
Find m and b.

Answer 1

Answer: m=-6 b=5

Explanation:

f(x)=mx+b

f(-3)=23 f(2)=7

`\displaystyle\\\left \{ {{23=(m)(-3)+b} \atop {-7=(m)(2)+b}} \right. \ \ \ \ \left \{ {{23=-3m+b\ \ \ \ (1)} \atop {-7=2m+b\ \ \ \ (2)}} \right.`

Subtract equation (2) from equation (1):

-30=5m

Divide both parts of the equation by 5:

-6=m

Thus, substitute m=-6 in (2):

-7=(-6)(2)+b

-7=-12+b

-7+12=-12+b+12

5=b

Hence,

y=-6x+5

Answer 2

b = 8 , m = - 5

Explanation:

For this question we can use simulteanous equations to solve for m and b.

We first come up with 2 equations.

Given the first condition:

23 = -3m + b

b - 3m = 23 (Equation 1)

Now the Second Condition:

-7 = 2m + b

b + 2m = -7 (Equation 2)

Now, we will use Equation 1 - Equation 2 to eliminate b to solve for m.

-3m - (+2m) = 23 - ( - 7)

- 5m = 30

m = 30 ÷ -6 = -5

Now we substitute m into Equation 1 to solve for b.

b - 3(- 5) = 23

b + 15 = 23

b = 23 - 15 = 8