Fill in the blanks in each of the following
The curves y = 4x2 + 2x – 8 and y = x3 – x + 13 touch each other at the point_____.
Given the first curve is y = 4x2 + 2x – 8
Now applying first derivative, we get
Now applying the sum rule of differentiation and the differentiation of the constant term is 0 we get
Now applying the power rule of differentiation we get
This is the slope of the first curve; let this be equal to m1.
⇒ m1=8x+2……(i)
Given the second curve is y = x3 – x + 13
Now applying first derivative, we get
Now applying the sum rule of differentiation and the differentiation of the constant term is 0 we get
Now applying the power rule of differentiation we get
This is the slope of the second curve; let this be equal to m2.
⇒ m2=3x2-1……(ii)
Now when the curve touch each other, there slope must be equal, i.e.,
m1=m2
⇒ 8x+2=3x2-1
⇒ 3x2-8x-1-2=0
⇒ 3x2-8x-3=0
Splitting the middle term, we get
⇒ 3x2+x-9x -3=0
⇒ x(3x+1)-3(3x+1)=0
⇒ (3x+1)(x-3)=0
⇒ (3x+1)=0 or (x-3)=0
Substituting in both the curves equation we get
For first curve, y = 4x2 + 2x – 8
For second curve, y = x3 – x + 13
Thus at both the curves do not touch
Substituting x=3 in both the curves equation we get
For first curve, y = 4x2 + 2x – 8
⇒y=4(3)2+2(3)-8
⇒y=4(9)+6-8=34
For second curve, y = x3 – x + 13
⇒y= (3)3 – (3) + 13
⇒y=27-3+13=37
Thus at x=3 both the curves do not touch
So the curves y = 4x2 + 2x – 8 and y = x3 – x + 13 do not touch each other.