Differentiation 5 - Gradient of a Curve
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Transcript of Differentiation 5 - Gradient of a Curve
Differentiation 5
Application of Differentiation – Gradient of a Curve
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Differentiation
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Tangent and Normal
If A(x1, y1) is a point on a line y = f(x), the gradient of the line (for a straight line) or the gradient of the tangent of the line (for
a curve) is the value of dy
dx when x = x1.
Gradient of tangent at A(x1, y1):
gradient of tangentdy
dx
Equation of tangent: 1 tangent 1( )y y m x x
Gradient of normal at A(x1, y1):
normaltangent
1m
m
1gradient of normal
dydx
Equation of normal : 1 1( )normaly y m x x
Example 1 (Find the equation of tangent )
Given that 2
4y
(3x 1)
. Find the equation of the
tangent at the point (1,1).
[Ans : y=‐3x+4]
Example 2 (Find the equation of normal)
Find the gradient of the curve 7
y3x 4
at the
point (‐1, 7). Hence, find the equation of the normal to the curve at this point. [clone SPM 1998]
[Ans : 21y –x –148 =0]
Differentiation
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Example 3 (Find the coordinates given gradient of normal) Find the coordinates of the point on the curve, y=(4x – 5)2 such that the gradient of the normal
to the curve is 1
8.
[Clone SPM 2006 P1]
[Ans : (1,1)]
Example 4 (Combination of tangent and another straight line) A curve has a gradient function of kx2 – 7x, where k is a constant. The tangent to the curve at the point (1, 4) is parallel to the straight line y + 2x ‐1 =0. Find the value of k.
[clone SPM 2005 ]
[ Ans : k=5]
Differentiation
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Example 5 (Combination of normal and another straight line) The normal to the curve y=x2 + 3x at the point P is parallel to the straight line y = ‐x + 12 Find the equation of the normal to the curve at the point P.
[Clone SPM 2008 P1]
[Ans : y=‐x‐3]
Example 6 (Combination of normal and another straight line) The straight line 4y + x = h is the normal to the curve y=(2x‐5)2‐2 at the point A. Find (a) the coordinates of point A and the value of h, (b) the equation of tangent at point A. [clone SPM 2000]
[Ans : (a) A(3,‐1) , h=‐1 ; (b) y=4x‐13]
Differentiation
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Example 7
In the diagram, the straight line PR is normal to
the curve 2x
y 1 2
at Q. Find the value of k.
[clone SPM 2005 P2]
[Ans : k=8]
Example 8 (Tangent perpendicular to another straight line) The tangent to the curve y=2x2+px+q at the point (1, 4) is perpendicular to straight line 7y+x‐14=0. Find the values of p and q.
[Ans : p=3, q=‐1]