tan 100° + tan 125° + tan 100° tan 125° is equal to

tan⁡100∘+125∘=tan⁡100∘+tan⁡125∘1−tan⁡100∘tan⁡125∘∴tan⁡225∘=tan⁡100∘+tan⁡125∘1−tan⁡100∘tan⁡125∘i.e., 1=tan⁡100∘+tan⁡125∘1−tan⁡100∘tan⁡125∘i.e., tan100° + tan 125° + tan 100° tan 125° = 1