Answer:
f(x) = 8.917x³ + 2x² + 0.083x - 7
Step-by-step explanation:
f(x)= y
Let the coefficients of x³, x², x be a, b, c and the constant be d
y= ax³ + bx² + cx + d
When y = -65, x = -2
-65= a(-2)³ + b(-2)² + c(-2) + d
-65= -8a + 4b - 2c + d ...eq. 1
When y = -14, x = -1
-14= a(-1)³ + b(-1)² + c(-1) + d
-14= -a + b - c + d ...eq. 2
When y = -7, x = 0
-7= a(0)³ + b(0)² + c(0) + d
-7 = d ...eq.3
When y = 4, x = 1
4= a(1)³ + b(1)² + c(1) + d
4= a + b + c + d ...eq. 4
when y = 78, x = 2
78 = a(2)³ + b(2)² + c(2) + d
78= 8a + 4b + 2c + d ...eq. 5
From eq. 3, d is - 7
putting d as - 7 in equations 1, 2, 4 and 5
In eq. 1,
-65= -8a + 4b - 2c - 7
-58= -8a + 4b - 2c ...eq. 6
In eq. 2
-14= -a + b - c - 7
-7= -a + b - c ...eq. 7
In eq. 4,
4= a + b + c - 7
11= a + b + c ...eq. 8
In eq. 5
78= 8a + 4b + 2c - 7
85= 8a + 4b + 2c ...eq.9
Subtracting eq. 9 from eq. 6
-143 = -16a - 4c... eq 10
subtracting eq. 8 from eq 7
-18= -2a - 2c
9= a + c
a = 9 - c ...eq 11
putting a as 9 - c in eq. 10
-143 = -16(9 - c) - 4c
-143 = -144 + 16c - 4c
1= 12c
c = 1/12 or 0.083
putting c as 1/12 in eq. 11
a = 9 - 1/12
a = 107/12 or 8.917
Putting a as 107/12 and c as 1/12 in eq. 8
11= 107/12 + b + 1/12
multiplying through by 13
132 = 107 + 12b + 1
132 - 108 = 12b
24= 12b
b = 24/12
= 2
Therefore, a= 8.917, b= 2, c= 0.083 and d = -7
f(x) = 8.917x³ + 2x² + 0.083x - 7
