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Solve 3x2 = −12x − 15. x = −4 ± 2i x = −4 ± i x = −2 ± 2i x = −2 ± i

diamong [38]

ANSWER

$x = - 2 \pm i$

EXPLANATION

We use the method of completing the squares.

The equation is
$3 {x}^{2} = - 12x - 15$

We rewrite the above equation to obtain;

$3 {x}^{2} + 12x = - 15$

We divide through by 3 to obtain;

${x}^{2} + 4x = - 5$

We add half the coefficient of
$x$

to both sides of the equation to get,

${x}^{2} + 4x + {2}^{2} = - 5 + {2}^{2}$

The right hand side is now a perfect square.

${(x + 2)}^{2} = - 1$

We now take square root of both sides to get;

$x + 2 = \pm \sqrt{ - 1}$

We add -2 to both sides,

$x = - 2 \pm \sqrt{ - 1}$

We simplify to obtain,

$x = - 2 \pm i$

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3 years ago

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How do I solve this?

podryga [215]

Answer:

$3078.8in^3$

Step-by-step explanation:

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4 0

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The _____ function is the most basic function in a family of functions.

grandymaker [24]

Answer:

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Step-by-step explanation:

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2 years ago

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Mrs. Martini is 6 years more than 3 times as old as Tony. Eight years ago, she

zalisa [80]

Mrs Martini age is 42 years and Tony age is 12 years

Step-by-step explanation:

The given is:

Mrs. Martini is 6 years more than 3 times as old as Tony
Eight years ago, she was 2 years less than 9 times as old as he was then

Assume that Tony is x years old now

∵ Mrs. Martini is 6 years more than 3 times as old as Tony

∵ Tony is x years old

- Multiply the age of Tony by 3 and add 6 to the product

∴ The age of Mrs Martini = 3 x + 6

8 years ago

- Subtract 8 from the age of each one

Tony age = (x - 8)

Mrs Martini age = (3 x + 6) - 8 = 3 x + 6 - 8 = 3 x - 2

∵ Eight years ago, Mrs Martini was 2 years less than 9 times as old

as Tony was then

- Multiply Tony age by 9 and subtract 2 from the product

∵ Tony age from 8 years ago = x - 8

∵ Mrs Martini age from 8 years ago = 3 x - 2

∴ 9(x - 8) - 2 = 3 x - 2

- Simplify the left hand side

∴ 9 x - 72 - 2 = 3 x - 2

- Add like terms

∴ 9 x - 74 = 3 x - 2

- Subtract 3 x from both sides

∴ 6 x - 74 = -2

- Add 74 to both sides

∴ 6 x = 72

- Divide both sides by 6

∴ x = 12

∵ x represents the age of Tony

∴ Tony is 12 years old

∴ 3 x + 6 is the age of Mrs Martini

- Substitute x by 12

∵ 3(12) + 6 = 36 + 6 = 42

∴ Mrs Martini is 42 years old

Mrs Martini age is 42 years and Tony age is 12 years

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6 0

2 years ago