Page:Elementary algebra (1896).djvu/383

LOGAKITHMS. 365 should increase the number corresponding to the logarithm 2.8222 by .0003 .0006 or 3 6 of .0001.

Thus the number corresponding to the logarithm 2.8222 = .0664 the number corresponding to the logarithm 2.8225 = .0664 Correction, .00005 = .06645

EXAMPLES XXXVIII. b.

Find the common logarithms of the following:

1. 50.  2. 203.   3. 6.73. 4. .341. 5. 0.045. 6. 5265. 7. 12345. 8. 0.010203. 9. 354.076.

Find the numbers corresponding to the following common logarithms:

10. 1.8156. 11. 2.1439. 12. 4.0022. 13. 1.9131. 14. 3.8441. 15. 7.4879-10.

447. Cologarithms. The logarithm of the reciprocal of a number is called the cologarithm of that number.

Thus colog 210 = log 210 = log 1 - log 210.

Since log 1 = 0, we write it in the form 10 - 10 and then subtract log 210, which gives

colog 210 = (10 - 2.3222)- 10 = 7.6778 - 10.

Hence

Rule. To find the cologarithm of a number, subtract the logarithm of the number from 10 and write -10 after the result. 448. The advantage gained by the use of cologarithms is the substitution of addition for subtraction.