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10 votes
10 votes
If A+B+6=90° prove that Sin²A +
Sin²B+sin^2 C = 1- 2 sin A . sin B . sin C


User Ziu
by
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1 Answer

22 votes
22 votes

Answer:

Let "a", "b" and "с" be sides of the triangle ("с" is the longest side).

The triangle will be:

right if a² + b² = c²

аcute if a² + b² > c²

obtuse if a² + b² < c²

a.

a=3, b=4 and c=5

a² + b² = 3² + 4² = 9 + 16 = 25 and c² = 5² = 25

25 = 25 ⇒ right triangle.

b.

a=5, b=6 and c=7

a² + b² = 5² + 6² = 25 + 36 = 61 and c² = 7² = 49

61 > 49 ⇒ аcute triangle.

c.

a=8, b=9 and c=12

a² + b² = 8² + 9² = 64 + 81 = 145 and c² = 12² = 144

145 > 144 ⇒ аcute triangle.

User Andrea Nagy
by
3.2k points
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