Explain why the structure of DNA is described as a double helix

The double helix is the description of the structure of a DNA molecule. A DNA molecule consists of two strands that wind around each other like a spiral staircase. Each chain has a backbone in which a sugar (deoxyribose) and a phosphate group alternate.

 Double helix is the description of the structure of a DNA molecule. A DNA molecule consists of two strands that wind around each other like a twisted ladder. Each strand has a backbone made of alternating groups of sugar (deoxyribose) and phosphate groups.

Explanation:

x = 3, y = - 9

Step-by-step explanation:

5x + 5y = - 30 (1)

2x - y = 15

-y = 15 - 2x

y = 2x - 15 (2)

From equations (1) & (2)

5x + 5(2x - 15) = - 30

5x + 10x - 75 = - 30

15x = 75 - 30

15x = 45

x = 45/15

x = 3

Plug x = 3 in equation (2)

y = 2*3 - 15

y = 6 - 15

y = - 9

Therefore,

x = 3, y = - 9

or

(x, y) = (3, - 9)