If three sides of the triangle are given as 32 cm, 34 cm and 34 cm, then the…
20172017
If three sides of the triangle are given as 32 cm, 34 cm and 34 cm, then the area of the triangle is:
- A.
500 cm²
- B.
480 cm²
- C.
450 cm²
- D.
475 cm²
Attempted by 43 students.
Show answer & explanation
Correct answer: B
Concept
For a triangle with all three sides known, the area equals one-half times the base times the corresponding height. When two sides are equal (isosceles), the perpendicular dropped from the apex to the unequal side bisects that side, so its height can be found by the Pythagoras theorem: (slant side)² = (half-base)² + (height)².
Application
The sides are 32 cm, 34 cm and 34 cm. Two sides are equal (34 = 34), so the triangle is isosceles with base 32 cm and equal sides 34 cm.
Drop a perpendicular from the apex to the 32 cm base; it bisects the base into two parts of 16 cm each.
Apply Pythagoras in one right half: height² = 34² − 16² = 1156 − 256 = 900, so height = 30 cm.
Area = ½ × base × height = ½ × 32 × 30 = 16 × 30 = 480 cm².
Cross-check
Heron's formula gives the same result independently. Semi-perimeter s = (32 + 34 + 34) ÷ 2 = 50. Area = √(s(s−a)(s−b)(s−c)) = √(50 × 18 × 16 × 16) = √230400 = 480 cm². Both methods agree, confirming the area is 480 cm².