Help! giving brainlest! Which advancement in mathematics contributed to improvements in algebra?

the use of formulas to show data
the use of vertical and horizontal axes
the development of multiplication
the substitution of letters for unknown numbers

3. republican abraham lincoln

4. south carolina

5. charleston, south carolina

6. confederates

7. minie bullet - made defense even safer, it spun faster, traveled further and was five times more accurate than any single-man weapon. able to kill at half a mile, it was the largest contributor to battle wounds

      or the the gatling gun - the most successful of several rapid-fire guns that were born before the war. its efficiency in killing only made war more deadly.

idk which one u learned about. pick one.

8. the south was fighting to maintain its way of life, whereas the north was fighting to maintain a union. so they had will, and the north were fighing on unfamiliar territory

9. union had the large population, people to fight in the war and work in the factories to make war materials, industrial base, the factories to make these war materials. the union also was wealthier than the confederacy and could finance the war.

10. stonewall jackson

11. chancellorsville

12. gettysburg

13. sherman

some of these might be wrong but i tried my best.   : )

the french revolution was when many people were persecuted for disagreeing or making separate government