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Home > Maths I > Relationships > Formulae

Maths I

Formulae

Evaluating a formula (continued)

Have a look at this worked example before going on to try the questions.

Example 3

An electrician used the formula below to find the total resistance in an electrical circuit.

R_T = {{R_1R_2} \over {(R_1 + R_2)}}

Where R_T is the total resistance

R_1 and R_2 are resistors in the circuit

Calculate the resistance in the circuit when R_1 is 4 and R_2 is 6

We are told R_1 = 4 and R_2 = 6

Put these values into the formula above

R_T = {{4 \times 6} \over {(4 + 6)}} = {24 \over 10 }= 2.4

Now try these questions.

Question

Use the formula in Example 2 to find the total resistance in the circuit when

\;{R_1} = 3 and \;{R_2} = 6

Answer

R_T = {{3 \times 6} \over {(3 + 6)}} = {18 \over 9} = 2

Question

Y = {{X(1 + T)} \over {(X + T)}}

Find the value of \;Y when \;X = 4 and \;T = 6.

Answer

Y = {{4(1 + 6) \over (4 + 6)} = {(4 \times 7) \over 10} = {28 \over 10} = 2.8}

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