8 SOME APPLICATIONS

The formula for the perimeter of a rectangle can be written P = 2(l + w).

So to solve "Find the length of the rectangle that has a perimeter of 45cm

                  and a width of 5cm."

Formula                                         P = 2(l + w)

Substitute the given values     45 = 2(l + 5)

Divide by 2 on each side       22·5 = l + 5

Subtract 5 on each side        17·5 = l

Another similar example, mathematically,

An isosceles triangle has two angles each of aº and a third angle of 44º. Calculate the value of a.

8A For each of the following write a suitable equation and solve it to work out:-

  1. the length of a rectangle that has a perimeter of 30cm and a width of 7cm.
  2. the length of a rectangle that has a perimeter of 66cm and a width of 14cm.
  3. the width of a rectangle that has a perimeter of 48cm and a length of 18cm.
  4. the width of a rectangle that has a perimeter of 53cm and a length of 17cm.
  5. the size of the equal angle of an isosceles triangle that has a third angle of 54º
  6. the size of the equal angle of an isosceles triangle that has a third angle of 28º
  7. the size of the third angle of an isosceles triangle that has two angles each of 28º
  8. the size of the third angle of an isosceles triangle that has two angles each of 71º

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