tolong dijawab pakai cara! nnti sy jdikn jwbn trbaik.

[tex]a) \: \:x\sqrt{2} = \sqrt{128} \: \: \: \: x = 8 \\ b) \sqrt{ {(x \sqrt{2} )}^{2} + {x}^{2} } = \sqrt{2 {x}^{2} + {x}^{2} } = \sqrt{3 {x}^{2} } = x \sqrt{3} = 8 \sqrt{3} \\ c)6 {x}^{2} = 6 \times 64 = 384 \: {cm}^{2} [/tex]

Bangun Ruang.

simbol ^ = pangkat

a.
rumus:
panjang diagonal sisi kubus = √r^2 + r^2
panjang diagonal sisi kubus = √2r°2
panjang diagonal sisi kubus = r√2

panjang diagonal sisi kubus = √128
r√2 = √128
r = √128 ÷ √2
r = √64 = 8
jadi panjang rusuk kubus = 8cm

b.
rumus;
panjang diagonal ruang kubus = √(r√2)^2 + r^2
panjang diagonal ruang kubus = √2r^2 + r^2
panjang diagonal ruang kubus = √3r^2
panjang diagonal ruang kubus = r√3

DF = diagonal ruang kubus
DF = r√3 = 8√3cm

c.
rumus:
luas permukaan kubus = 6 × r^2

luas = 6 × 8^2 = 6 × 64 = 384cm^2