tan(70°) = 2.75. To get this value when we know that tan(35°) = 0.70, we apply the tan double angle formula:
tan(2θ) = 2×tan(θ) / [1 - tan²(θ)].
Plugging in θ = 35°, we obtain
tan(70°) = 2 × 0.70 / [1 - 0.70²] = 2.75, as claimed.