The slope of tangent to the curve x = t2 + 3t – 8, y = 2t2 – 2t – 5 at the point (2, –1) is:
Given equation of curve is x = t2 + 3t – 8, y = 2t2 – 2t – 5
x = t2 + 3t – 8
Differentiating on both sides with respect to t, we get
Applying the sum rule of differentiation, we get
We know derivative of a constant is 0, so above equation becomes
Applying the power rule we get
y = 2t2 – 2t – 5
Differentiating on both sides with respect to t, we get
Applying the sum rule of differentiation, we get
We know derivative of a constant is 0, so above equation becomes
Applying the power rule we get
Now we know,
Now substituting the values from equation (i) and (ii), we get
As given the curve passes through the point (2,-1), substituting these values in given curve equation we get
x = t2 + 3t – 8
⇒ 2= t2 + 3t – 8
⇒ t2 + 3t – 8-2=0
⇒ t2 + 3t – 10=0
Splitting the middle term we get
⇒ t2 + 5t-2t – 10=0
⇒ t(t+ 5) -2(t+5)=0
⇒ (t+ 5) (t-2)=0
⇒ t+5=0 or t-2=0
⇒ t=-5or t=2……….(iii)
y = 2t2 – 2t – 5
⇒ -1=2t2 – 2t – 5
⇒ 2t2 – 2t – 5+1=0
⇒ 2t2 – 2t – 4=0
Taking 2 common we get
⇒ t2 – t – 2=0
Splitting the middle term we get
⇒ t2 – 2t +t– 2=0
⇒ t(t– 2)+1(t– 2)=0
⇒ (t– 2)(t+1)=0
⇒ (t– 2)=0 or (t+1)=0
⇒ t=2 or t=-1……..(iv)
So from equation (iii) and (iv), we can see that 2 is common
So t=2
So the slope of the tangent at t=2 is given by
Therefore, the slope of tangent to the curve x = t2 + 3t – 8, y = 2t2 – 2t – 5 at the point (2, –1) is
So the correct option is option B.