How many cubes are needed to build the base of this structure

5 cubes

Step-by-step explanation:

The figure consists of three layers.

The top layer consists of one cube (this cube is visible).

The second layer consists of 3 cubes (two of them are visible and one is not visible - placed under the cube of the top layer).

The third layer (base layer) consists of 5 cubes:

So, 5 cubes are needed to build the base of the figure.

step-by-step explanation:

4tyuiuygsugv15167889997q669a

xcvb nm you ugly

x = ±sqrt(10)

step-by-step explanation:

5 - 2x² = -15

subtract 5 from each side

5-5 - 2x² = -15-5

-2x^2   = -20

divide by -2 on each side

-2x^2   /-2= -20/-2

x^2 =10

take the square root on each side

sqrt(x^2 )=±sqrt(10)

x = ±sqrt(10)

check:

5 - 2x² = -15

+sqrt(10)

5 - 2(sqrt(10))² = -15

5 -2(10) = -15

5 -20 = -15

-15 = -15

-sqrt(10)

5 - 2(-sqrt(10))² = -15

5 -2(10) = -15

5 -20 = -15

-15 = -15