Changing the subject with more complex formula
I can apply an understanding of inverse operations to a complex formula in order to make a specific variable the subject.
- Year 9
Changing the subject with more complex formula
I can apply an understanding of inverse operations to a complex formula in order to make a specific variable the subject.
Lesson details
Key learning points
- With more complex formula, it is important to apply the inverse operations in the right order.
- The subject can be thought of as the unknown you are trying to find the value of.
- Instead of finding a value though, you will find an expression that the unknown is equal to.
Keywords
Subject of an equation/formula - The subject of an equation/a formula is a variable that is expressed in terms of other variables. It should have an exponent of 1 and a coefficient of 1.
Common misconception
The subject of a formula is just the first term in the formula.
Draw attention to the variety of equations and formulae used in the lesson.
Licence
Prior knowledge starter quiz
6 Questions
Q1.The subject of a formula is a variable expressed in terms of the other __________.
Q2.$$x^2$$ is not the subject of the equation $$x^2=9-y^2$$. Why not?
Q3.Which of these are rearrangements of the equation $$5e-7=2d$$ ?
Q4.Which two inverse operations should you perform to both sides to solve the equation $$6x+7=49$$?
Q5.Select the expressions that are equivalent to $${1\over3}(y-5)$$.
Q6.Match each expression to its description.
$$5d+2$$ -Â $$d \text{ }$$ multiplied by $$5$$ then add $$2$$
$${d\over5}+2$$ -Â $$d\text{ }$$ divided by $$5$$ then add $$2$$
$${{d+5}\over2}$$ -Â $$d\text{ }$$ add $$5$$ then divided by $$2$$
$$2d+5$$ -Â $$d\text{ }$$ multiplied by $$2$$ then add $$5$$
$$5(d+2)$$ -Â $$d\text{ }$$ add $$2$$ then multiplied by $$5$$
$${1\over5}(d+2)$$ -Â $$d\text{ }$$ add $$2$$ then divided by $$5$$
Assessment exit quiz
6 Questions
Q1.Performing the inverse operation $$\div7$$ would make $$x$$ the __________ of the equation $$7x=y.$$
Q2.Some Oak pupils are rearranging the equation $$5e-f=14$$ to make $$e$$ the subject. Who has a correct rearrangement?
Q3.Match each formula to the correct rearrangement with $$d$$ the subject.
$${{d+6}\over8}=e$$ -Â $$d=8e-6$$
$$8d+6=e$$ -Â $${{e-6}\over8}=d$$
$${{d-6}\over8}=e$$ -Â $$d=8e+6$$
$$8(d+6)=e$$ -Â $${e\over8}-6=d$$
$${d\over8}-6=e$$ -Â $$d=8(e+6)$$
Q4.Make $$x$$ the subject of the equation $$y=7x^2$$.
Q5.Make $$x$$ the subject of the equation $$y={7\over{x^2}}$$.
Q6.Match each formula to the correct rearrangement with $$x$$ the subject.
$$2x=\sqrt{y}$$ -Â $$x={\sqrt{y}\over2}$$
$$2\sqrt{x}=y$$ -Â $$x=({y\over2})^2$$
$$\sqrt{2x}=y$$ -Â $$x={y^2\over2}$$
$$2x^2=y$$ -Â $$x=\sqrt{y\over2}$$
$$(2x)^2=y$$ -Â $$x={{\sqrt{y}}\over2}$$