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stiv31 [10]
3 years ago
13

The sum of three numbers in g.p. is 21 and the sum of their squares is 189. find the numbers.

Mathematics
1 answer:
sashaice [31]3 years ago
3 0
Let the three gp be a, ar and ar^2
a + ar + ar^2 = 21 => a(1 + r + r^2) = 21 . . . (1)
a^2 + a^2r^2 + a^2r^4 = 189 => a^2(1 + r^2 + r^4) = 189 . . . (2)
squaring (1) gives
a^2(1 + r + r^2)^2 = 441 . . . (3)
(3) ÷ (2) => (1 + r + r^2)^2 / (1 + r^2 + r^4) = 441/189 = 7/3
3(1 + r + r^2)^2 = 7(1 + r^2 + r^4)
3(r^4 + 2r^3 + 3r^2 + 2r + 1) = 7(1 + r^2 + r^4)
3r^4 + 6r^3 + 9r^2 + 6r + 3 = 7 + 7r^2 + 7r^4
4r^4 - 6r^3 - 2r^2 - 6r + 4 = 0
r = 1/2 or r = 2
From (1), a = 21/(1 + r + r^2)
When r = 2:
a = 21/(1 + 2 + 4) = 21/7 = 3
Therefore, the numbers are 3, 6 and 12.
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The following set of numbers 2√3, 4√2, and 3√5, can be the measures of the sides of an obtuse triangle.

A triangle is a polygon with three sides and three vertices.

To know if a set of number is a valid measure of the sides of a triangle, it must follow the Triangle Inequality Theorem which states that the sum of any two sides must be greater than the third side, such that a + b > c, a + c > b, and b + c > a.

let a = 2√3, b = 4√2, and c = 3√5

a + b > c     2√3 + 4√2 > 3√5     9.12 > 6.71     True

a + c > b     2√3 + 3√5 > 4√2     10.17 > 5.66    True

b + c > a     4√2 + 3√5 > 2√3     12.37 > 3.46     True

To know what type of triangle based on the length of its side:

1. Take the sum of the squares of the two smaller sides.

(2√3)^2 + (4√2)^2 = 44

2. Compare it to the square of the largest side.

(3√5)^2 = 45

44 < 45

If the sum of the squares of the 2 is larger than the square of the 3rd, it is an acute triangle.

if they are equal, it is a right triangle

if they are smaller, then it is an obtuse triangle.

Hence, 2√3, 4√2, and 3√5 can be the measure of the sides of an obtuse triangle.

To learn more about types of triangle based on side lengths: brainly.com/question/13619935

#SPJ4

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1 year ago
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