Write an equation to represent the number puzzle. Use x as the

Mathematics

1 answer:

k0ka [10]2 years ago

7 0

<h3>The equation is:</h3><h3> $x^2 - 7x + 12 = 0$ </h3><h3>The number is 3 or 4</h3><h3><em><u>Solution:</u></em></h3>

Given that,

7 added to the square of a number is equal to 7 times the number, minus 5

Let "x" be the unknown number

From given,

7 added to square of x = 7 times the x minus, 5

$7 + x^2 = 7x - 5$

Solve the above equation

$x^2 -7x +7+5 = 0\\\\x^2 - 7x + 12 = 0$

Split the middle term

$x^2 -3x - 4x + 12 = 0\\\\Group\ the\ expressions\\\\(x^2-3x) -(4x - 12) = 0\\\\Take\ the\ common\ factor\ out\\\\x(x -3) -4(x -3) = 0\\\\(x-3)(x-4) = 0$

We have two solutions

x - 3 = 0

x = 3

And

x - 4 = 0

x = 4

Thus number is 3 or 4

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Find the sum of the first 20 terms of the arithmetic sequence 4, -4, -12, -20

Vsevolod [243]

Answer:

The sum of the first 20 terms is -1440.

Step-by-step explanation:

We want to find the sum of the first 20 terms of the arithmetic sequence:

4, -4, -12, -20...

The sum of an arithmetic sequence is given by:

$\displaystyle S=\frac{k}{2}(a+x_k)$

Where <em>k</em> is the number of terms, <em>a</em> is the initial term, and <em>x</em>_<em>k</em> is the last term.

Since we want to find the sum of the first 20 terms, <em>k</em> = 20.

Our initial term <em>a</em> is 4.

Our last term is also the 20th term as we want the sum of the first 20 terms.

To find the 20th term, we can write an explicit formula for our sequence. The explicit formula for an arithmetic sequence is given by:

$x_n=a+d(n-1)$

Where <em>a</em> is the initial term, <em>d</em> is the common difference, and <em>n</em> is the <em>n</em>th term.

Our initial term is 4. From the sequence, we can see that our common difference is -8 since each subsequent term is eight less than the previous term. Therefore:

$x_n=4-8(n-1)$