Answer:
84
Step-by-step explanation:
let a be the 1's digit and b the 10's digit, then
a = 2b ← twice the 10's digit, thus
sum = 2b + b = 12, that is
3b = 12 ( divide both sides by 3 )
b = 4
and a = 2b = 2 × 4 = 8
The 2 digit number is 84
The answer is 14%
Cost of meal is 100%: $18.50 is 100%
Tip is x%: $2.59 is x
Make a proportion:
$18.50 : 100% = $2.59 : x
x = 100% * $2.59 : $18.50
x = 14%
X² + 8x +y² - 2y -64 =0
We see that the equation has x² and y² . Also we see that coefficients in front of x² and y² are equal. So this is an equation of the circle.
(x² + 8x) +(y² - 2y) -64 =0
(x² + 8x) +(y² - 2y) = 64
We need to complete square for x and y groups, that means it should be written in form (a+b)² or (a-b)².
Expressions in parenthesis we will write as a²+/-2ab+b², to write it after as (a+/-b)², because a²+/-2ab+b² = (a+/-b)²
(x² + 2*4x) +(y² - 2*1y) = 64
(x² + 2*4x+4²) +(y² - 2*1y+1²) = 64+4²+1²
(x+4)² + (y-1)²= 81 Sometimes this is called a standard form of the circle.
(x+4)² + (y-1)²= 9² Sometimes it is required to write like this.
And if you are studying circles,ellipses and hyperbolas, the standard form should look like
The fromula of a slope:

a) (-1, -8), (-7, -4)
substitute

b) (2.1, 3.8), (3.1, 7.6)
substitute
