# Lesson Notes By Weeks and Term - Junior Secondary School 3

CHANGE OF SUBJECT OF FORMULA

SUBJECT: MATHEMATICS

CLASS:  JSS 3

DATE:

TERM: 1st TERM

REFERENCE BOOKS

• New General Mathematics by M. F Macrae et al bk 3
• Essential Maths by AJS OluwasanmiBk 3

WEEK EIGHT

TOPIC: 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:

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: mx+c= y,    mx=y-c

X=  y-c

M

To find the value of X, X=    10-2

4

X= 8/4 =2

Evaluation: If I=  PRT

1. makep 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= mv-mu

T

Solution:   S=2¶r(r+h)

S=2¶r 2 +2¶rh

S- 2¶r 2 =2¶rh

S-2¶r2 =h

2¶r

1.   F =mv-mu

T

Cross multiply:  FT =mv-mu

FT =m(v-u)

FT

v-u       = m

EVALUATION

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

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
1. a = vu-t (b) a= v-u  (c) a = v+u

tt

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

6

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

1. Express n in terms of s, a, and L if S=n/2(a+L)

(a) n=2(a+L)    (b) n=  2S    (c) 2S-(a-L)

Sa+L

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

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

THEORY

1. Given L = arn-1, make a the subject of the formula.
2. If S +     2t          , make t the subject of the formula. Find the value of t if S=1, d= 2.

d