Let me try to solve it.
So twice the square of a number:
2x²
and
16 less than 10 times the number
16 - 10x
Let's combine both
2x² = 16 - 10x
Move right expression to the left and change sign
2x² +10x -16 = 0
We may now use quadratic formula for this.
x = (-b±√b²-4ac)/2a
where a = 2, b = 10 and c = -16
Replace a, b and c
x = (-10±√10² - 4(2 * -16))/2(2)
Multiply 2 and -16, 2 and 2, and get the square of 10
x = (-10±√100 - 4(-32))/4
Multiply -4 and -32
x = (-10±√100 + 128)/4
Add 100 and 128
x = (-10±√228)/4
Get square root of 228
x = (-10±15.0996688705415)/4
Break up expression
x = (-10 + 15.0996688705415)/4
Add
x = 5.0996688705415/4
Divide
x = 1.274917217635375
---
x = (-10 - 15.0996688705415)/4
Subtract
x = -25.0996688705415/4
Divide
x = -6.274917217635375
Now to check:
We are going to use the positive result except of the negative.
2(1.274917217635375)² = 16 - 10(1.274917217635375)
2(1.625413911823126143) = 16 - 12.74917217635375
3.250827823646252286 = 3.25082782364625
Almost the same as you can see except of the 2286 in the last from the left side.
I hope it helps.
