4. As shown in the figure, given that the area of a small triangle is 1, what is the sum of the areas of all the triangles in the figure?



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【Answer】 426
【Explanation】 Case analysis
1 $\triangle$: 36, area $1 \times 36=36$
4 $\triangle$s: 15 upright, 6 inverted, total 21, area $1 \times 4 \times 21=84$
9 $\triangle$s: 10 upright, 1 inverted, total 11, area $1 \times 9 \times 11=99$
16 $\triangle$s: 6 upright, area $1 \times 16 \times 6=96$
25 $\triangle$s: 3 upright, area $1 \times 25 \times 3=75$
36 $\triangle$s: 1 upright, area $1 \times 36=36$
Total area: $36+84+99+96+75+36=426$