Properties of Triangles 2 Question 5

5. If the angle of a triangle are 30 and 45 and the included side is (3+1)cm, then the area of the triangle is … .

(1988, 2M)

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Answer:

Correct Answer: 5. 1+32 sq cm 6. a>5

Solution:

  1. By sine rule, asinA=bsinB=csinC

3+1sin(105)=bsin30

b=(3+1)sin30sin105

Area of triangle

=12absin45=12(3+1)(3+1)sin30sin45sin105

=12(3+1)2(sin45cos60+cos45sin60)1212=142(3+1+23)1212+1232=(4+23)42(1+3)22=(1+3)22(1+3)=1+32sqcm



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