New
New
Year 11
Higher

Estimating the gradient of a curve

I can estimate the gradient of a curved part of the graph by considering the gradient of a straight line connecting two points.

New
New
Year 11
Higher

Estimating the gradient of a curve

I can estimate the gradient of a curved part of the graph by considering the gradient of a straight line connecting two points.

Lesson details

Key learning points

  1. The gradient of a curve can be estimated.
  2. You can estimate by drawing a straight line between two points on the graph.
  3. The closer the points, the more accurate the estimate is.

Common misconception

Pupils may estimate negative gradients incorrectly by drawing gradient triangles the wrong way round or ignoring the fact that the $$y$$ values are decreasing as $$x$$ increases.

Pupils should look at the shape of the graph between two points and decide if it is positive or negative before calculating. If $$y$$ is decreasing as $$x$$ increases then the gradient is negative.

Keywords

  • Gradient - The gradient is a measure of how steep a line is. It is calculated by finding the rate of change in the $$y$$-direction with respect to the positive $$x$$-direction.

Pupils can use this skill to estimate average speed from non-linear distance-time graphs. There is an example in learning cycle 2 but you may wish to use graphs from lessons 5 and 7 of this unit as further practice for pupils.
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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6 Questions

Q1.
Gradient is the __________.
Correct answer: measure of how steep a line is
measure of the length of a line
Correct answer: rate of change in $$y$$-direction with respect to positive $$x$$-direction
rate of change in $$y$$-direction with respect to negative $$x$$-direction
Q2.
What is the gradient of this line?
An image in a quiz
$$+2$$
$$+3$$
Correct answer: $$-4$$
$$-8$$
Q3.
What is the gradient of this line?
An image in a quiz
$$4$$
$$-6$$
$$-6/4$$
Correct answer: $$2\over3$$
$$3\over2$$
Q4.
What is the gradient of the line going through coordinate pairs $$(18,73)$$ and $$(50,233)$$?
Correct answer: $$5$$
$$1\over5$$
$$-{1\over5}$$
$$-5$$
Q5.
Which statements are true of this curve?
An image in a quiz
The gradient is positive.
Correct answer: The gradient is positive sometimes.
The gradient is negative.
Correct answer: The gradient is negative sometimes.
Correct answer: The gradient is zero sometimes.
Q6.
What is the gradient of the line going through coordinate pairs $$\left(-{{1}\over{4}},{{5}\over{3}}\right)$$ and $$\left({{7}\over{3}},-{{16}\over{5}}\right)$$?
$${{292}\over{155}}$$
Correct answer: $$-{{292}\over{155}}$$
$${{155}\over{292}}$$
$$-{{155}\over{292}}$$

6 Questions

Q1.
The gradient of the hypotenuse of the triangle is not the exact gradient of the curve between $$x=2$$ and $$x=6$$, it is only __________.
An image in a quiz
Correct answer: an estimate
a calculation
a computation
Correct answer: an approximation
Q2.
Estimate the gradient of this curve between $$x=2$$ and $$x=6$$
An image in a quiz
Correct Answer: 2, +2
Q3.
Estimate the gradient of this curve between $$x=-6$$ and $$x=-4$$
An image in a quiz
$$2$$
$$5\over2$$
Correct answer: $$-{{5\over2}}$$
$$-{{2\over5}}$$
$$-5$$
Q4.
What is wrong with using the coordinate pairs (-7, 12) and (-2, 1) to estimate the gradient of this curve?
An image in a quiz
Correct answer: The points are too far apart.
Nothing. It is quick and accurate to estimate this gradient this way.
Correct answer: The distance between the hypotenuse and the curve means it lacks accuracy.
The changes in $$x$$ and $$y$$ are not both $$+11$$
Q5.
Match the intervals to the estimated gradient of the curve in those intervals.
An image in a quiz
Correct Answer:$$x=0 \ \text{to} \ x=1$$,$$4$$

$$4$$

Correct Answer:$$x=1 \ \text{to} \ x=2$$,$$-4$$

$$-4$$

Correct Answer:$$x=2 \ \text{to} \ x=3$$,$$-6$$

$$-6$$

Correct Answer:$$x=3 \ \text{to} \ x=4$$,$$-2$$

$$-2$$

Correct Answer:$$x=4 \ \text{to} \ x=5$$,$$7$$

$$7$$

Q6.
The interval $$x=0$$ to $$x=$$__________ would be poor because it would give you an estimated gradient of $$0$$
An image in a quiz
Correct Answer: 2, 5