
c=αa+βb…..(1)a⋅c=αa⋅a+βb⋅a0=α+βcos15∘….(2)(1)⇒b⋅c=αa⋅b+βb⋅b⇒cos75∘=αcos15∘+β….(3)(2)&(3)⇒cos75∘=−βcos215∘+β β=sin215∘cos75∘=sin15∘1=3−122 (2) ⇒α=sin15∘−cos15∘=(3−1)−(3+1) ∴c=(3−1)−(3+1)a+(3−122)b Now $\begin{aligned}
& \alpha+\sqrt{2}(\sqrt{3}-1) \beta=\frac{-(\sqrt{3}+1)}{(\sqrt{3}-1)}+\frac{\sqrt{2}(\sqrt{3}-1) \cdot 2 \sqrt{2}}{\sqrt{3}-1} \
& =\frac{-(\sqrt{3}+1)^2}{2}+4 \
& =\frac{-3-1-2 \sqrt{3}+8}{2} \
& =2-\sqrt{3}
\end{aligned}$