# linear function equation?

what is a and b if

y=m*x^2

x1=4

x2=12

x3=b

y1=a

y2=18

y3=72

I need to get the answers: a=2, b=24.

how can get those answers can someone help me out, thank you.

### 2 Answers

- 冷眼旁觀Lv 72 months agoFavorite Answer
Equation of the curve: y = mx²

(x₁, y₁), (x₂, y₂) and (x₃, y₃) are the point lying on the curve.

Hence, (4, a), (12, 18) and (b, 72) lie on the curve.

(12, 18) lies on the curve. Put x = 12 and y = 18 into the equation y = mx²:

18 = m(12)²

18 = 144m

m = 18/144

m = 1/8

Equation of the curve: y = x²/8

(4, a) lies on the curve. Put x = 4 and y = a into the equation y = x²/8:

a = 4²/8

a = 2

(b, 72) lies on the curve. Put x = b and y = 72 into the equation y = x²/8:

72 = b²/8

b² = 576

b = ±√576

b = ±24

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- Pramod KumarLv 72 months ago
The correct way of writing your problem is --

Evaluate a and b if --

y = m x^2

Given that when -

x = 4 , y = a ........... (1)

x = 12, y = 18........(2)

x = b , y = 72.........(3)

Substitute these values in the given equation y = m x^2 one by one .

from (1)

=> a = m (4)^2 => a = 16 m ....... (A)

from (2) 18 = m (12)^2 => m = (18/144) = (1/8)

m = (1/8) ............. ( B)

From (1) and (2) a = 16/8 = 2 .................. Answer

Again, from (3)

72 = (1/8) (b)^2

=> b^2 = 72*8 => b = 24 Answer

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