1.quotient n.【數】商(the number resulting from the division of one number by another)

例：lf you divide 26 by 2,the quotient is 13.

2.raccoon n．浣熊

例：Raccoons are shy and active only at night.

3.racism n.種族歧視(racial prejudice or discrimination)；種族主義(a belief that race is the primary determinant of human traits and some races are superior to others)

詞根記憶：rac(e)（種族）+ism（……主義）——種族主義

同根詞：racist(n．種族主義者)

4.radiant a．輻射的：發光的(radiating rays or reflecting beams of light)；容光煥發的(marked by or expressive of love confidence, or happiness)

詞根記憶：radi(光線，射線)+ant—發光的—容光煥發的

例：a radiant smile燦爛的笑容

同根詞：radiation(n.發光，傳播)；radiator(n．散熱器)

5.radiate v.放射，輻射(to send out in or as if in rays)

詞根記憶：radi(光線)+ate—發光，放熱—放射，輻射

例：The national observatory has been observing x-rays radiated by compact stars for years.

派生詞：radiation(n．放射；放射物；放射線)

6.radical a．激進的(extreme, drastic)；n.激進分子(a person who is radical)

詞根記憶：radic(根)+aI—根本不講道理的—激進的

例：a radical feminist激進的女權主義者

派生詞：radically( ad.徹底地；激進地)

7.radioactive a．放射性的，有輻射能力的(of, caused by or exhibiting radioactivity)

詞根記憶：radi(輯射：光線)+o+active(活躍的)—發射光活躍的—放射性的

例：Calcium carbonate shells contain radioactive material.

8.radiocarbon n．放射性碳

聯想記憶：radio(無線的)+carbon(碳)—不經過實體傳播的碳—放射性碳

例：Using new radiocarbon dating techniques, it was determined that the charcoal from the Colorado site was at least 11,400 years old.

9.radiusi n．半徑(a line segment extending from the center of a circle or sphere to the circumference or bounding surface)

注意：diameter(n．直徑)；circumference(n．圓周)

例：The radius of the circle is 0.5 meter.