Change Of Subject Formulae

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In today’s Mathematics class, We will be discussing Change of Subject of Formula. We hope you enjoy the class!

 

CHANGE OF SUBJECT OF FORMULA

A formula is a general equation involving two or more unknowns. An example is the formula a = ¶r²  which gives the area of the circle in terms of its radius r. In this formula, a is called the subject of the formula.

 

Simplifying a formula by substitution

Example:

1. Given mx+c=y, express x in terms of m, c, and y. Find the value of x if y=10, c=2 and m is 4

Solution:

1)  mx+c= y,    mx=y-c

$x = \frac{y–c}{m}$

To find the value of X, when  y= 10 , m=4and c=2

 

X=$\frac{10–2}{4} = \frac{8}{4} = 2$

 

Evaluation: If I=  PRT

• Make p the subject and find the value of p if I = 10, R= 4, and T= 5.

 

 

CHANGING THE SUBJECT OF A FORMULA

When a variable which forms a part of the formula is made subject, we say we have changed the subject of the formula.

Examples:

1. In the formula S=2¶r(r+h), make h the subject.
2. Make m the subject if $F = \frac{mv – mu}{T}$

 

Solution:

1) S=2¶r(r+h)

S=2¶r ² +2¶rh

S- 2¶r ² =2¶rh

S-2¶r² =h

2¶r

 

 

2) $F = \frac{mv – mu}{T}$

Cross multiply:  FT =mv-mu

FT =m(v-u)

$$\begin{gathered} \frac{FT}{v–u} = m \\ m = \frac{FT}{v–u} \end{gathered}$$

 

 

EVALUATION

1. Make r the subject if V =¶r ²h
2. Make u the subject if 1/f =1/v + 1/u

 

READING ASSIGNMENT

1. Exam focus for J.S.C.E Pg. 212 -216
2. Essential Maths for J.S.S.3 Pg. 47-54

 

WEEKEND ASSIGNMENT

1. Express a in terms of u, v, and t in v= u+at
   • • (a)  a = vu-t
     •  (b) a= v-u
     •  (c) a =  $\frac{v+u}{t}$

 

2.   If Z=2p +3, find the value of Z when p=1. (a) Z=2, (b) Z= 5, (c) Z =7
3. In the relation X = $\frac{m–6y}{6}$  , how would you write m in terms of x and y?

(a) m=x-6   (b) m = 6x -6y (c) m =6x +6y

4. Express n in terms of s, a, and L if $S = \frac{n}{2(a+L)}$

$\left(a\right) n = \frac{2(a+L)}{Sa+L} \left(b\right) n = \frac{2S}{a +L} \left(c\right) n = 2S – (a–L)$

5. Make U the subject if V² = U²  +2as.

(a) U= V ² -2as   (b) U = (V ² -2as) ²     (c)       V²  – 2a

 

THEORY

1. Given L = ar^n-1, make a the subject of the formula.
2. If S + $\frac{2t}{d}$, make t the subject of the formula. Find the value of t if S=1, d= 2.

 

 

We have come to the end of this class. We do hope you enjoyed the class?

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In our next class, we will be talking about Measure of Central Tendency. We are very much eager to meet you there.

 

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