The formula for straight-line depreciation is:
\[
\text{Depreciation per year} = \frac{\text{Initial cost} - \text{Salvage value}}{\text{Useful life}}
\]
Substitute the values:
\[
\text{Depreciation per year} = \frac{10,00,000 - 50,000}{10} = \frac{9,50,000}{10} = 95,000
\]
The value of the machine at the end of 7 years is:
\[
\text{Book value at end of 7 years} = \text{Initial cost} - 7 \times \text{Depreciation per year}
\]
\[
\text{Book value at end of 7 years} = 10,00,000 - 7 \times 95,000 = 10,00,000 - 6,65,000 = 3,35,000
\]
Thus, the book value of the machine at the end of the 7th year is \( \boxed{3,35,000} \).