log2(5√2) = log2 5 + log2 √2 = log2 5 + 1/2
log7 10 / log7 2 = log2 10 = log2 (2 · 5) = 1 + log2 5
log2 5 + 1/2 - (1 + log2 5) = log2 5 + 1/2 - 1 - log2 5 = -1/2