[121.] Problem I.
[122.] Problem II.
[123.] Operation.
[124.] Demonstration.
[125.] Remark.
[126.] Problem III.
[127.] Method II.
[128.] Operation.
[129.] Demonstration.
[130.] Method III.
[131.] Operation.
[132.] Demonstration.
[133.] Remark.
[134.] Problem IV.
[135.] Problem V.
[136.] Operation.
[137.] Demonstration.
[138.] Problem VI.
[139.] Method II.
[140.] Operation.
[141.] Demonstration.
[142.] Method III.
[143.] CHAP. VI.
[144.] Prob. I.
[145.] Prob. II.
[146.] Demonstration.
[147.] Corollary.
[148.] Method II.
[149.] Operation,
[150.] Demonstration.