Which expression represents 81 decreased by an unknown number?

a. 81−a

b. 81a

c. 81÷a

d. 81 + a

Choice A

Step-by-step explanation:

The correct answer is choice A. The equation 81 - a is doing exactly what the question is asking for. It represents 81 minus an unknown number, with the unknown number being shown as a.

The answer is A. 81 - a

Step-by-step explanation: decreased is practically a synonym for subtract, so we use the symbol for subtraction (-). 81 decreased by an unknown number, which then we use a symbol to show the unknown variable, like a letter. So (a) represents the unknown number. Hence, 81 decreased by an unknown number becomes 81 - a.

5x + 3y = - 4

step-by-step explanation:

the equation of a line in standard form is

ax + by = c ( a is a positive integer and b, c are integers )

express the line first of all in slope- intercept form

y = mx + c ( m is the slope and c the y-intercept )

to calculate m use the gradient formula

m = ( y₂ - y₁ ) / ( x₂ - x₁ )

with (x₁, y₁ ) = (7, - 3) and (x₂, y₂ ) = (4, - 8)

m = = -

y = - x + c ← is the partial equation

to find c substitute either of the 2 points into the partial equation

using (4, - 8 ), then

- 8 = - + c ⇒ c = -

y = - x - ← in slope-intercept form

multiply all terms by 3 to eliminate the fractions

3y = - 5x - 4 ( add 5x to both sides )

5x + 3y = - 4 ← in standard form

5

step-by-step explanation: