Given that there is a triangle △ A B C with the lengths 7 , 1 1 and 1 4 while the size of the angles are unknown.
The area of the triangle can be simplified as x y
What is x + y ?
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S=(7+11+14/2) Heron's formula states that the area of a triangle is = \sqrt(S(S-a)(S-b)(S-c)) Plug in the numbers and you get \sqrt((16)(9)(5)(2))=3 4 \sqrt(5*2) =12\sqrt(10) since the area of a triangle can be expressed as the square root of y times x. x=12 y=10 x+y=22
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By using Heron's formula, we have s = 2 7 + 1 1 + 1 4 = 1 6 , where s is the semi perimeter of the triangle. Then, the area of the triangle would be
( 1 6 ) ( 1 6 − 7 ) ( 1 6 − 1 1 ) ( 1 6 − 1 4 )
⟹ ( 2 4 ) ( 3 2 ) ( 5 ) ( 2 )
⟹ 2 2 × 3 1 0
⟹ 1 2 1 0
Comparing with x y , we arrive x + y = 2 2 , which is our desired answer.
your solution is 9 5 % same as mine
95%
By the way, area of any triangle actually also can be found by using Cosine Rule and the formula below.
T = 2 1 a b sin C .
So, let AB=7, BC=11, AC=14. By cosine rule, we have
1 4 2 = 7 2 + 1 1 2 − 2 ( 7 ) ( 1 1 ) cos ∠ B
2 6 = 1 5 4 cos ∠ B
7 7 1 3 = cos ∠ B
∠ B = cos − 1 7 7 1 3
which is approximately about 8 0 ∘ 1 6 ′ . So, substitute the values, we arrive
T = 2 1 × 7 × 1 1 × sin 8 0 ∘ 1 6 ′
T = 3 7 . 5 sin 8 0 ∘ 1 6 ′
T ≈ 3 7 . 9 5 ≈ 1 2 1 0
So, as you can see, the area of the triangle also can be determined by the way above. But, since we need the most accurate answer (otherwise we can't find x + y ), so this way is not very encouraged.
By using the Heron's Formula, we can find the area by getting S = 2 7 + 1 1 + 1 4 = 1 6
Then we get 1 6 × ( 1 6 − 7 ) × ( 1 6 − 1 1 ) × ( 1 6 − 1 4 ) = 1 4 4 0
1 4 4 0 = 1 4 4 × 1 0
Since the square root of 1 4 4 is 1 2 , we can simplifly it to 1 2 1 0
Therefore, x = 1 2 , y = 1 0
x + y = 1 2 + 1 0 = 2 2
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Plug the values into Heron,s Formula: A r e a = s ( s − a ) ( s − b ) ( s − c ) where s = 2 a + b + c So s = 2 7 + 1 1 + 1 4 = 2 3 2 = 1 6 A r e a = 1 6 ( 1 6 − 7 ) ( 1 6 − 1 1 ) ( 1 6 − 1 4 ) = 1 6 × 9 × 5 × 2 = 1 4 4 × 5 × 2 = 1 2 1 0 So x = 1 2 and y = 1 0 and x + y = 1 2 + 1 0 = 2 2