Answer:
14cm
Step-by-step explanation:
All side lengths in a cube will be 7 as the properties of a cube are such that all the side lengths are the same.
Think of the longest line in a cube as a hypotenuse on a triangle.
[tex]7^{2} + 7^{2} = c^{2}[/tex]
49 + 49 = [tex]c^{2}[/tex]
[tex]c^{2}[/tex] = 98
c = [tex]\sqrt{98}[/tex]
[tex](\sqrt{98})^{2} + (\sqrt{98} )^{2}[/tex] = [tex]c^{2}[/tex]
[tex]c^{2}[/tex] = 98 + 98
[tex]c^{2}[/tex] = 196
c = [tex]\sqrt{196}[/tex]
c = 14
The longest line in a cube that has a side length of 7cm is 14cm.
